Distributed feedback (DFB) lasers typically include a first facet which has a partial reflector (i.e., an anti-reflective (AR) coating) and a second facet which has a total reflector (i.e., a high reflective (HR) coating). While the second facet with the total reflector reflects more than 90% of the light in the laser, this configuration results in low threshold current. Further, the second facet is typically fabricated using a mechanical process (e.g., a cleaving process) which is not precise (i.e., has high tolerances). As a result, the phase of the light reflected from the total reflector back towards the partial reflector is uncertain. This grating phase change can cause instability in the HR/AR DFB laser that can result in mode hopping where the wrong wavelength is amplified.
However, using two facets that both have partial reflectors (e.g., the AR coating) can result in low efficiency. That is, although DFB lasers that use AR/AR coatings are inherently less susceptible to grating phase changes at the facets, they suffer from reduced efficiency where significant amounts of light exit from both facets in contrast to the HR/AR DFB laser where almost all the light exits through the facet with the AR coating but not the facet with the HR coating.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.